At this time, in the automotive field, contact systems are used in electrical plug connections in which the individual contacts are attached to the electrical lines in a first working step, and in a second working step the plug is latched in the contact chamber. In this connection, essentially two primary latching mechanisms are used. In the so-called “lance contacts”, flexible metallic elements of the contact latch in recesses or undercuts in the contact chamber. In the so-called “clean body contacts”, elements of the contact chamber spring in recesses or undercuts of the contacts and in this manner latch to the contacts. In multi-part chamber systems, two latching types are known for clean body contacts. In multi-part chamber systems, two latching types are known for clean body contacts. The first latching type is characterized in that the latching arm is linked to the contact chamber wall at the height of the contact shoulder, and the latching hook engages in a contact undercut, near the contact opening. The latching arm grows, as it were, in the plug-in direction and when it stops, it is essentially stressed axially by pressure. The second latching type is characterized in that the latching arm is linked to the contact chamber wall at the height of the contact shoulder, and the latching hook reaches over the contact shoulder or engages in a corresponding opening near the contact shoulder. The latching arm grows, as it were, opposite to the plug-in direction and when it stops, it is essentially stressed in tension. In both cases the latching arms with their latching hooks are usually extruded with their latching hooks in the contact carrier lower part as parts of the contact chamber walls. Making available the latching hooks is only one task of the contact chamber in the contact carrier lower part. The part of the contact chamber in the contact carrier lower part should, in addition, guide contacts through chamber walls, and thereby ensure a correct clearance of the contacts. In addition, the contact chamber should form the plug-in funnel for the contact pins of the matching side. The technical requirements for stable latching hooks, secure contact guides and a stable plug-in funnel run counter to present customer requirements for ever smaller contact clearances at contact sizes that remain the same or are even increasing. At this time, there are limits to further closer approach to each other of the contact chambers from an extrusion and mold release technology point of view, since both the wall thickness of the injection tools and the plastic wall thickness have been carried to the limit.
In the contact chambers of multi-pole plug connections, usually the primarily latched contacts are checked additionally by a so-called secondary locking with respect to their correct position in the contact chamber, and if the primary latching fails, they are additionally secured at their correct insertion depth. In multi-pole contact connections, in this instance, in many cases so-called premounted and transversely shiftable secondary locking plates are used, which, in a prelatched position, first permit the unhindered assembling of the contacts all the way into the contact chambers, and which then, at the end of the assembling procedure, are shifted by at least one-half contact chamber width transversely to the contact chamber axes. Using their locking projections that project laterally into the contact chambers, the secondary locking plates, in this context, on the one hand elicit information on the correct depth of insertion of the contacts, and, on the other hand, ensure additional locking.